In many parts of the world, desalinated sea water and desalinated brack water are the only sources of potable water.
Another source of water which, at the moment, is largely untapped is contaminated water flowing from factories and flowing to sewage treatment works. These two sources are usually, at most, treated to bring the water to what is called “river quality” and this water is then allowed to flow into a river and is hence not available for re-use.
There are various methods of desalination in use and a common one uses semi-permeable material which allows water to pass through but retains any remaining solids and the dissolved solids. Desalination is usually preceded by a filtration step to remove the bulk of the solids.
Such desalinators use what are called “membranes”. Each membrane comprises a perforated core tube and a plurality of rectangular leaves which are fixed to, and then wound around, the core tube. Each leaf is closed along three edges and open along the fourth. It is along the fourth edge that the leaf is secured to the core tube. A spacer is provided within each leaf to prevent it collapsing. Spacers are also provided between leaves. Water to be treated flows in the dissolved solids retention passages between the leaves, permeates through the material of the leaves into the permeate passages within the leaves and flows from the permeate passages to the inside of the tube. Brine flows along the membrane from one end to the other, remaining in the retention passages and exits through a brine outlet.
Each membrane is within an elongate cylindrical casing. The pressure within each casing is of the order of 40 to 60 bar or higher. This results in significant forces being applied to the end closures which seal the ends of the casing. Elongate casings of similar form are used to filter liquids and remove solid particles therefrom. The pressure existing in casings used for filtration is generally lower than that used in desalination but nevertheless the forces generated are still capable of dislodging the end closures.
The object of the present invention are to provide an improved casing and an improved method of manufacturing such a casing.